1. Field of the Invention
The invention concerns polymerizable compounds suitable for forming bodies for generating heat from radiant luminous energy, particularly but not exclusively from the energy radiated by the sun.
The invention also concerns methods of preparing such compounds.
The invention is further concerned with the application of such compounds to the formation of generating bodies, especially solar panels and devices for heating bodies of water in open-top containers such as swimming pools.
2. Description of the Prior Art
A known way of capturing radiant luminous energy, in particular energy radiated by the sun, is to place blackened panels such as metal sheets painted matt black, in the path of the radiated energy. The types of paint used do not behave like ideal black bodies at all wavelengths, however, from the visible spectrum to the far infra red, where the majority of the energy radiated in the solar spectrum is concentrated. The principal reasons for this are the low thermal conductivity of the paint and the variation of the thickness which absorbs energy with wavelength. In fact, absorption of the shortest wavelengths, which lie in the visible spectrum and which carry about 48% of the radiant energy, takes place in a surface layer in poor thermal contact with the supporting metal sheet, while the thickness of the black layer is too small to absorb the incident energy of long wavelength, which is relected. Increasing or decreasing the thickness of the black layer can only improve operation at one end of the spectrum at the expense of degrading operation at the other end.
For work on an experimental scale generating bodies have been developed which are made by sintering an intimate mixture of a finely divided absorbent black charge and a finely divided diffusing white charge. The black charges which can be sintered are in the main oxides of titanium, copper, manganese, iron, nickel and cobalt, while the main sinterable white charges are oxides of silicon, beryllium, magnesium, zirconium, and thorium. The mechanism of absorption is believed to be as follows:
The black charges are intrinsically close to ideal black bodies, while diffusion of the radiation in the sintered mass by the white charges traps the radiation, in the manner of a theoretical black body consisting of a hole in a hollow sphere. As a result, absorbtion is virtually complete for all wavelengths of radiation, and occurs practically uniformly throughout the mass of the generating body. Also the thermal conductivity of such oxides is much greater than that of paint.
The technique of sintering involves high pressure and high temperature processes, however, so that it is not possible to make large or complex items in this way except at exorbitant cost. The products are fragile and often stand up poorly to thermal shock, and there is very little scope for coupling them thermally in an efficient manner to other items. Finally, the technique of sintering is hardly compatible with highly efficient and relatively cheap black and white charges such as graphite in the case of the black charges and double carbonates of calcium and magnesium in the case of the white.